1. Field of the Invention
This invention relates to a machining apparatus having a degree of freedom of machining of three axes or greater.
Herein, the term “axes” or “an axis” is defined as a portion of a machining apparatus that functions as the reference line or plane of a movement for machining, for example, the rotary shaft of a swivel table, the slideway of a slide table, etc. The degree of freedom of movement for machining is one for each of the “axes”.
2. Description of the Related Art
A machining apparatus for applying cutting machining, grinding machining, or the like to an optical element and a die for the formation thereof is known (refer to JP 2003-39294, for example).
In this connection, in order to generate a complex curved surface corresponding to an aspherical surface of an optical element with a high accuracy, a degree of freedom of machining of two or less is insufficient, and a degree of freedom of machining of three or greater is required. However, in a machining apparatus having a degree of freedom of machining of three axes or greater for the generating of an optical surface which is a free surface, whichever of cutting or grinding the machining may be, it becomes necessary, a shaping process in which a machined surface is generated while a number of through machining steps are being connected one after another; therefore, it has a feature such that it requires a very long time, which is not found in the machining by means of any other kind of machining apparatus. For that reason, in order to carry out a machining for generating a free surface with a high accuracy and a high efficiency, it is necessary to actualize the following necessary conditions more sufficiently than a conventional machining apparatus.
Necessary Conditions for Actualizing High Accuracy
(1) There is a requirement for making higher the control accuracy of the machine, and for that purpose, it is necessary to control a workbench (a slide table or a swivel table) driven by a high-speed servomechanism with a high accuracy achieved by the improvement of the resolving power of the position measurement of each of the axes, or to lighten the driven workbench by the use of a material having a small specific weight so that it may comply with the drive instruction of the servomotor at a high speed.
(2) Because the machine has a block structure with each of the axis portions placed over one another in two or three stages, which makes the overall stiffness tend to become lowered for the structural reason, it is necessary to make higher the stiffness of each of the axis portions as much as possible, and for that purpose, it becomes important to lower the viscosity of the pressure transmission medium of the static-pressure slide, or to use a material having a high Young's modulus.
(3) It is also very important to make the machine not subject to the temperature variation of the environment, and in a case where a static-pressure slide is used, it is important to lower the viscosity of the pressure transmission medium in order to suppress a useless heat generation at the static-pressure surface, and also it is important to select a material having a small coefficient of linear expansion for each of the members.
(4) It is necessary to shorten the machining time for the purpose of making it possible to finish the machining before the environment variation becomes large and carrying out the machining with a high efficiency; therefore, the following things are necessary: to comply with the high resolution of the position measurement by making higher the speed of the servomechanism in order to drive the axis at a high speed, and to lower the viscosity of the pressure transmission medium so that the lowering of stiffness of the static-pressure surface and a vibration may not be generated.
(5) In order to prevent the influence of the vibration due to the vibration of the floor and the oscillation of the machine body itself, it is necessary, an active vibration-reducing table or the like which practices a control in such a way that it detects and suppresses a vibration in an active manner.
However, heretofore, it has never existed a machining apparatus having a degree of freedom of machining of three axes or greater that can achieve the compatibility of a high accuracy of an order of sub-micron with a high efficiency of machining.